Ice cores have certainly done their share for climate science, but nobody’s perfect. While they contain wildly useful samples of ancient air and proxy records of temperature, linking the two together is harder than you might expect. Once you get down to fine-scale questions of timing, that difficulty becomes important.

Several studies that have looked at the start of the warming out of the last ice age have concluded that the temperature began to rise several centuries before carbon dioxide increased. This week, a new study in Science shows that may not be the case.

The complications arise from the way that air is trapped in ice. The ice, of course, forms from snow compressed by the weight of the snow on top of it. Above the ice, then, it’s possible for air to move between the bits of snow (or partially compacted “firn”). So while this year’s snow (from which temperature is determined) is found at the surface, it won't be encapsulated as much as 100 meters below. That means that when you analyze a layer from an ice core, the age of the ice and the age of the air bubbles are offset. If we want to know whether temperature rose before CO2, we have to know which layer of ice corresponds to which layer of air bubbles.

This has typically been estimated with the use of a “firn densification model.” Given parameters like the proxy measurements of temperature and the snow accumulation rate (from the layer thicknesses), the model calculates the depth at which the firn would have turned into ice—the depth at which the air would have been locked in. But there’s another way of extracting that information from the ice core more directly. Beyond a certain depth, the air is isolated from the effects of wind at the surface. In this stagnant zone, the air mainly moves by simple molecular diffusion.

Of the nitrogen gas that makes up about 78 percent of the atmosphere, some molecules contain atoms of nitrogen-14’s heavier brother, nitrogen-15. Simply because of gravity, the heavier nitrogen-15 will be over-represented near the bottom of the diffusion zone and therefore also in this ice. The thicker the diffusion zone, the more prevalent nitrogen-15 will be. (You can think of a footrace between a fast and slow person—the longer the sprint, the greater the fast person’s lead at the finish.)

So by measuring the ratio of nitrogen isotopes in the air bubbles, glaciologists can infer how big the offset between contemporaneous ice and air must have been.

Using this technique, a group of European researchers analyzed the timing of events at the end of the last ice age in the EPICA Dome C ice core from Antarctica. The original study that examined the record of carbon dioxide in this core put the start of the warming 800±600 years before the rise in carbon dioxide 18,000 years ago. Using the new age scale, however, the new study sees the change in CO2 leading by a statistically insignificant 10±160 years. In other words, as near we can determine, they happened at the same time.

The study also looked at three prominent wiggles in the 8,000 years that followed. They largely showed the same behavior—with CO2 and temperature changing at about the same time—though temperature appeared to lead by at least several decades in one instance.

In a related perspective, Oregon State’s Edward Brook writes, “In many ways, these results are not surprising, given the coupled nature of the carbon cycle and climate and the fact that oceanic processes around Antarctica probably play a key role in glacial-interglacial CO2 dynamics. They are important, however, because they improve our understanding of when CO2 changed with respect to temperature in the ice core record.”

It wasn’t really puzzling when we originally found that CO2 might have followed temperature by several centuries. The overall pacing of the ice ages is clearly controlled by cycles in Earth’s orbit, with the effects of the resulting changes in sunlight being amplified by greenhouse gases, among other factors. (Many smaller scale events, of course, were driven by things like ocean circulation changes, volcanic eruptions, and solar variation.) At the same time, it’s not a shock to learn that the two were more synchronized.

But the new information is still helpful. Knowing how long it took for the carbon cycle to respond can help researchers examine the processes that allowed it to respond. Current models focus on diminishing sea ice, which allowed CO2 to vent from the Southern Ocean, along with changes in ocean circulation.

When we figure out why things happened the way they did, we gain an understanding of how the climate system works. As that picture comes into sharper focus, we discover what we can expect to happen in the future—depending, of course, on the choices we make.

AbstractA number of records commonly described as showing control of climate change by Milankovitch insolation forcing are reexamined. The fraction of the record variance attributable to orbital changes never exceeds 20%. In no case, including a tuned core, do these forcing bands explain the overall behavior of the records. At zero order, all records are consistent with stochastic models of varying complexity with a small superimposed Milankovitch response, mainly in the obliquity band. Evidence cited to support the hypothesis that the 100 Ka glacial/interglacial cycles are controlled by the quasi-periodic insolation forcing is likely indistinguishable from chance, given the small sample size and near-integer ratios of 100 Ka to the precessional periods. At the least, the stochastic background ‘‘noise’’ is likely to be of importance.

Now, before rushing rash conclusions, I haven't tracked down the obligatory criticisms of Wunsch's analysis. But that glaciation cycle forcing still remained a debatable topic as recently as a decade past, only emphasizes the extremely delicate balance between temperature and greenhouse gasses (CO2) that prevailed during the Pleistocene -- the likes of which we are doing our damnedest never to see again.

I guess this further emphasises the importance of identifying and understanding the positive feedback mechanisms in our climate system, as any tipping points we thought we were edging towards may be a lot closer than we realise.

I feel this issue (is CO2 rising *before* or *after* temperature) to be quite important.After all, we have some huge and costly policy in place in order to control CO2 emission, due to its impact on temperature rise. They'd better be correct.

In the past, i've been learned that CO2 "global warmimg effect" would trigger a temperature increase.See, the consequence seems clearly established : more CO2, get more C°.And as a proof, i've been showed such graphs, where CO2 & temperature variations are correlated. The link between the CO2 and temperature rise was spectacular shown within Al Gore's "Inconvenient truth" movie.

Since CO2 has now reached a level never seen in human existence, and keep increasing fast, this was an especially worrying situation.

But what if CO2 rise is, in fact, a *consequence* of increased temperature ? (for example due to increased biomass activity) This would change the whole picture. The gloomy prophecies linking the end of humanity to the sole CO2 rise would fall short of one of their major arguments. And that's why i've been very puzzled to notice such "lag" between temperature and CO2 rate, with CO2 rate "following", not leading temperature.

Apparently, the new study tries to make CO2 "less late", but it's still behind temperature. Which makes me doubt : "which one is the chicken, which one is the egg ?".

This would be an academic argument, if not for the dire consequences on several industries (Power supply being one of the affected ones today, with dubious, if not outright outrageous, "advantages" (financial incentives) provided to unproven technology alternatives).

Note : I'm not saying that CO2 has "no greenhouse effect". That's not the point.The "established" link between CO2 and temperature created the perception that CO2 is "THE indicator to follow", because it is THE trigger for temperature rise.If this link is severed, then it might be that CO2 is a mere contributor, maybe even a pretty minor one, turning our attention towards more meaningful directions.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

There is NO progression of CO2 increase and temperature increase which disproves 2, UNLESS you were to see temperatures decrease across a substantial CO2 level increase. That is never apparent in these records. Either temperature increases, then CO2 begins to increase, and they both increase together for a while, then both level off, and then both fall, or the increase is near simultaneous.

It is perfectly feasible that say Milankovich cycle causes a temperature increase which CO2 release then feeds back on and amplifies, giving a leading temperature signal, or that CO2 starts to increase and temperature IMMEDIATELY follows (which is pretty close to what we observe today). In other words both of your 'examples' are exactly consistent with the evidence and ARE AGW. The Sun (Milankovich cycle) warms the surface slightly, RELEASING CO2, which then causes a further temperature rise, OR Volcanoes release CO2 into the air, which warms the Earth, causing a feedback release of more CO2 and more warming. The actual heat released by volcanoes BTW is trivial by comparision to what the Sun shines down on the top of the Earth's atmosphere. Sufficient vulcanism to heat the surface directly would require unprecedented volcanic activity, so much that it would have flooded vast areas, ended most life, etc (See Siberian Traps or Deccan Traps for effects of super vulcanism).

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time.

You seem to be ignoring basic planetology here. Something drove either an increase in CO2 or an increase in temperature, either of which then led to the other. I don't see how this would disprove AGW, seeing as how we are indeed something.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

There is NO progression of CO2 increase and temperature increase which disproves 2, UNLESS you were to see temperatures decrease across a substantial CO2 level increase. That is never apparent in these records. Either temperature increases, then CO2 begins to increase, and they both increase together for a while, then both level off, and then both fall, or the increase is near simultaneous.

It is perfectly feasible that say Milankovich cycle causes a temperature increase which CO2 release then feeds back on and amplifies, giving a leading temperature signal, or that CO2 starts to increase and temperature IMMEDIATELY follows (which is pretty close to what we observe today). In other words both of your 'examples' are exactly consistent with the evidence and ARE AGW. The Sun (Milankovich cycle) warms the surface slightly, RELEASING CO2, which then causes a further temperature rise, OR Volcanoes release CO2 into the air, which warms the Earth, causing a feedback release of more CO2 and more warming. The actual heat released by volcanoes BTW is trivial by comparision to what the Sun shines down on the top of the Earth's atmosphere. Sufficient vulcanism to heat the surface directly would require unprecedented volcanic activity, so much that it would have flooded vast areas, ended most life, etc (See Siberian Traps or Deccan Traps for effects of super vulcanism).

Do you know what the A stands for in AGW? Nothing here is hinting at anthropocentric sources. That is to say the human-cause release of CO2. It does not include natural CO2 release. We know the oceans and peat bogs outgas CO2 when they warm. You have to prove that the anthropocentric component is causal and not just present for the ride.

EDIT: I just looked it up and since we started counting CO2, we're about 1ppm per year. For AGW to be true, this 1ppm increase must be substantially anthropocentric and must be responsible for warming. it does not pass basic scrutiny that our planet is vulnerable to a 1ppm increase, which is approaching a 0.25% increase of CO2, per year. We'd live on one fragile planet if that was the case. But we know CO2 has been both higher and lower and animal life thrived over all those ranges.

I feel this issue (is CO2 rising *before* or *after* temperature) to be quite important.After all, we have some huge and costly policy in place in order to control CO2 emission, due to its impact on temperature rise. They'd better be correct.

In the past, i've been learned that CO2 "global warmimg effect" would trigger a temperature increase.See, the consequence seems clearly established : more CO2, get more C°.And as a proof, i've been showed such graphs, where CO2 & temperature variations are correlated. The link between the CO2 and temperature rise was spectacular shown within Al Gore's "Inconvenient truth" movie.

Since CO2 has now reached a level never seen in human existence, and keep increasing fast, this was an especially worrying situation.

But what if CO2 rise is, in fact, a *consequence* of increased temperature ? (for example due to increased biomass activity) This would change the whole picture. The gloomy prophecies linking the end of humanity to the sole CO2 rise would fall short of one of their major arguments. And that's why i've been very puzzled to notice such "lag" between temperature and CO2 rate, with CO2 rate "following", not leading temperature.

Apparently, the new study tries to make CO2 "less late", but it's still behind temperature. Which makes me doubt : "which one is the chicken, which one is the egg ?".

This would be an academic argument, if not for the dire consequences on several industries (Power supply being one of the affected ones today, with dubious, if not outright outrageous, "advantages" (financial incentives) provided to unproven technology alternatives).

Note : I'm not saying that CO2 has "no greenhouse effect". That's not the point.The "established" link between CO2 and temperature created the perception that CO2 is "THE indicator to follow", because it is THE trigger for temperature rise.If this link is severed, then it might be that CO2 is a mere contributor, maybe even a pretty minor one, turning our attention towards more meaningful directions.

I don't understand your concern. We KNOW that increased temperature leads to CO2 entering the atmosphere. So we KNOW that the melting of contenental ice sheets CERTAINLY caused CO2 release. There's no either/or thing here though, once the CO2 started to be released it caused higher temperatures and more CO2 release etc until some natural limit was reached. This is perfectly consistent with temperature leading CO2 (to some limit, but 600 years seems to within the bounds of reason). The point is that if WE release CO2 by burning coal and oil we are starting the same sort of cycle, except in our case CO2 leads temperature, once the thing gets started it doesn't matter how or why the initial kick happened, the climate spins up into a new stability zone at some higher temperature (math jargon ommited).

Of course it is certainly interesting to know how big the temp/CO2 lag actually was, if there was one at all. It is more a matter of "all information is useful" though, this data isn't going to prove or disprove anything, CO2's function as a GHG is in any case already proven many times over. Don't be fooled by the denialist PR machine, we're already tracking a quarter of a billion PR $ a year being spent on this in the US alone. The energy sector will do ANYTHING to spread doubt.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

Actually it's been known for a long time now that global temp always changes before CO2 levels change. There's a lag of few hundred years between the temp change and CO2 level changes due to the fact that it takes that long to warm and cool the oceans causing them to release and absorb CO2. Ice ages are a complicated issue as well. It's not as simple as looking at CO2 levels.

Isn't the point of this article that the CO2 release happens around the same time? Or have I completely mis-read it?

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

Actually it's been known for a long time now that global temp always changes before CO2 levels change. There's a lag of few hundred years between the temp change and CO2 level changes due to the fact that it takes that long to warm and cool the oceans causing them to release and absorb CO2. Ice ages are a complicated issue as well. It's not as simple as looking at CO2 levels.

Isn't the point of this article that the CO2 release happens around the same time? Or have I completely mis-read it?

Do you know what the A stands for in AGW? Nothing here is hinting at anthropocentric sources. That is to say the human-cause release of CO2. It does not include natural CO2 release. We know the oceans and peat bogs outgas CO2 when they warm. You have to prove that the anthropocentric component is causal and not just present for the ride.

Did you think climate scientists had just, I don't know, not thought to consider natural sources of greenhouse gasses? Because we're actually not ignorant of the carbon cycle.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

There is NO progression of CO2 increase and temperature increase which disproves 2, UNLESS you were to see temperatures decrease across a substantial CO2 level increase. That is never apparent in these records. Either temperature increases, then CO2 begins to increase, and they both increase together for a while, then both level off, and then both fall, or the increase is near simultaneous.

It is perfectly feasible that say Milankovich cycle causes a temperature increase which CO2 release then feeds back on and amplifies, giving a leading temperature signal, or that CO2 starts to increase and temperature IMMEDIATELY follows (which is pretty close to what we observe today). In other words both of your 'examples' are exactly consistent with the evidence and ARE AGW. The Sun (Milankovich cycle) warms the surface slightly, RELEASING CO2, which then causes a further temperature rise, OR Volcanoes release CO2 into the air, which warms the Earth, causing a feedback release of more CO2 and more warming. The actual heat released by volcanoes BTW is trivial by comparision to what the Sun shines down on the top of the Earth's atmosphere. Sufficient vulcanism to heat the surface directly would require unprecedented volcanic activity, so much that it would have flooded vast areas, ended most life, etc (See Siberian Traps or Deccan Traps for effects of super vulcanism).

Do you know what the A stands for in AGW? Nothing here is hinting at anthropocentric sources. That is to say the human-cause release of CO2. It does not include natural CO2 release. We know the oceans and peat bogs outgas CO2 when they warm. You have to prove that the anthropocentric component is causal and not just present for the ride.

No, all I have to demonstrate is what the climate sensitivity is. If you followed any of the actual science you would know that this is in the range of 1.5-4.5 Kelvins for a doubling of CO2, and that we've seen a 0.8K rise so far in about the last 150 years. This is all attributable and easily explained by human-generated CO2 to a level of greater than 99% confidence. There's no "along for the ride", we emit CO2 and that CO2 warms the Earth and then more CO2 is emitted because of that. Knowing how much and what the timing is clearly helps us know the sensitivity number better, but you're still failing to come up with any sort of logic supporting your statements.

I'd also just note that when talking about pre-historic CO2 levels we aren't talking about anthropogenic anything, we are talking about purely looking at feedback effects and natural forcings. Whatever we as humans do is ON TOP OF THAT, which still makes it important and no findings about specific pre-historic periods (certainly not in the range of what this study shows) will change that a whole lot. It is just refining numbers.

As for climate scientists, I note that there have been a number of studies that show forcings are less than half of of what is used in IPCC models.

Citation?

Scorp1us wrote:

I also note that IPCC models have gratuitously predicted far more warming than observed. So they apparently don't know the carbon cycle well enough to make a reasonable prediction. That's science. prediction, experiment, results, refinement. They have a lot more refining to do.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time.

You seem to be ignoring basic planetology here. Something drove either an increase in CO2 or an increase in temperature, either of which then led to the other. I don't see how this would disprove AGW, seeing as how we are indeed something.

Easy. If changing global temps drive CO2 levels then CO2 levels clearly do not drive changes in global temp. You get it now? Maybe Corbyn can explain it to you:

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

Actually it's been known for a long time now that global temp always changes before CO2 levels change. There's a lag of few hundred years between the temp change and CO2 level changes due to the fact that it takes that long to warm and cool the oceans causing them to release and absorb CO2. Ice ages are a complicated issue as well. It's not as simple as looking at CO2 levels.

Isn't the point of this article that the CO2 release happens around the same time? Or have I completely mis-read it?

Um, remember, you have to add "On my Fantasy Planet" to the start of g0m3r619's statements. Most of the things he states are pure nonsense he scraped off some denier site somewhere. Specifically, as you noted, it isn't "known for a long time now that global temp always changes before CO2 levels change" at all, we are far from knowing this. Again, EVEN IF THERE IS A LAG, that has nothing to do with the fact that when the CO2 hits the atmosphere it causes warming. The link between CO2 and warming has been established at the highest levels of certainty, changes in the timing in these cores will probably give us better info to establish sensitivity numbers from, etc, but the fundamental causal linkage and the magnitude of the effect are well established.

Do you not realize that CO2 release rates during non-human-involved warming periods does nothing to the question of CO2 as a agent in warming? A single CO2 molecule converts more infrared radiation into heat than a single nitrogen molecule, and we are increasing the ratio of CO2 in the atmosphere. Where is the extra heat from our extra atmospheric CO2 in your model? Until you find a reason why more CO2 won't result in more heat, like a temperature buffer effect, more CO2=more heat. This is not a new concept.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time. The only result that can be had is that a common factor - the sun or volcanoes are responsible. The sun would have warmed the oceans, releasing CO2 as well as raising the global temperature. Or submerged volcanoes would have heated the planet and oceans while releasing CO2. Seeing as we don't have that much volcanic evidence, I am left to conclude the sun is the driver.

Actually it's been known for a long time now that global temp always changes before CO2 levels change. There's a lag of few hundred years between the temp change and CO2 level changes due to the fact that it takes that long to warm and cool the oceans causing them to release and absorb CO2. Ice ages are a complicated issue as well. It's not as simple as looking at CO2 levels.

Isn't the point of this article that the CO2 release happens around the same time? Or have I completely mis-read it?

He's a known troll around here. Please disregard his ravings.

I'm a troll for not agreeing with your baseless belief that human activity is driving climate changes? Nice...

No, you're a troll for posting the same arguments over and over again in every AGW article's comments even though you've been shown time and time again that those arguments have been debunked.

So they basically disproved anthropocentric global warming. Whatever increased the temperature, also increased the CO2 at the same time.

You seem to be ignoring basic planetology here. Something drove either an increase in CO2 or an increase in temperature, either of which then led to the other. I don't see how this would disprove AGW, seeing as how we are indeed something.

Easy. If changing global temps drive CO2 levels then CO2 levels clearly do not drive changes in global temp. You get it now? Maybe Corbyn can explain it to you:

Why is that true?CO2 causes a rise in temps, and that causes the release of more CO2, which causes further heating..OrXYZ causes a rise in temps, and that causes the release of CO2, which causes further heating..

I'm not sure how you came to the conclusion that CO2 cannot be a driver... It doesn't have to be, but that doesn't mean it cannot.